Fluidized beds are frequently utilized for the treatment --by heat or in some other manner--of bulk material whose particles are to remain suspended in a given environment for an extended period. The state of suspension is maintained by a carrier gas which tends to keep the particles in motion and separated from one another. This separation is important for the desired reaction, e.g. a combustion of carbon granules which may widely vary in particle size.
Not infrequently, however, smaller particles react only incompletely or not at all before being entrained out of the treatment zone by the carrier gas. This problem has been recognized in commonly owned European patent application 0,042,095, published 23 Dec. 1981, which proposes as a solution therefor the provision of a treatment chamber with an apertured bottom overlying a wind box through which carrier gas is admitted into the chamber, the latter being subdivided by several upright partitions into a plurality of juxtaposed compartments including at least one bounded by a substantially solid portion of the chamber bottom. The partitions have openings through which the mass can circulate in vertical loops after being fed from above into the compartment or compartments into which the carrier gas is more or less prevented from penetrating; the pressure differential between the latter compartments and the adjoining ones, subject to the updraft of the rising carrier gas, causes the aforementioned circulation. The European application also discloses deflectors of triangular cross-section, disposed at the bottom of any down-flow compartment, which direct the descending particles into the adjoining compartments under or through the intervening partitions. The latter, as further described in that application, may be formed by louvres slanting down toward the more or less aperture-free bottom portions.
While the described system is generally satisfactory, we have found that its mode of operation is not always reliable to the extent required under certain conditions, e.g. when it is necessary to burn residual carbon particles in a mass of ash.